x++: Returns the old value of x.
It matters which only when the return value is used:
x++; and ++x; are the same.
Increment operators are similar to Java.
Things like x + ++x are not well-defined in C.
In the context of C, increments are better able to create bizarre programs.
An expression has a value. If it changes any of its variables, that is called a side effect.
x++ and ++x have the different values but the same side-effect. x+1 has the same value as ++x, but no side effect.